A brainstorming session by some of the West Coast's leading salmon experts has pointed to ocean conditions in the Strait of Georgia and the possible impact of fish farms as the most likely causes of a collapse of Fraser River sockeye stocks.

But the two-day think tank, organized by Simon Fraser University and the Pacific Fisheries Resource Conservation Council, concluded Wednesday that the government needs to do more research to solve the puzzle.

In the meantime, conference spokesmen Mark Angelo and John Reynolds said, the Department of Fisheries and Oceans should manage the salmon harvest much more cautiously.

"It's a bit like trying to figure out what happened in a plane crash," Mr. Reynolds said of the difficulty scientists face in trying to piece together why the Fraser run so suddenly and totally collapsed.

"There's a lot of [research]work to be done, but in the meantime we need to take an even more precautionary approach [to the harvest]" said Mr. Angelo, chair of the conservation council and head of the fish and wildlife program at the B.C. Institute of Technology. The conference was prompted by the shocking decline of the Fraser sockeye run over the summer, when the return, forecast at 11 million salmon, turned out to be about one million.

Mr. Reynolds, who holds the Tom Buell BC Leadership Chair in Salmon Conservation at SFU, said as devastating as the collapse was - the lowest return in more than 50 years - the long-range trend is even more troubling.

"The productivity of these fish … has been declining," he said. "Fraser River sockeye are almost unable now to replace themselves."

Historically, the Fraser River had salmon runs of nearly 40 million sockeye until rail-road construction caused a massive slide at Hell's Gate Canyon in 1913, cutting off fish from their spawning beds. By 1916, fewer than two million sockeye were returning to the Fraser.

Stocks rebuilt through the 1940s and 1950s, and by 1958, the run had climbed back to about 20 million fish. Then stocks fell again, most probably because of overfishing, and through the 1960s, runs of four million to eight million became typical. An improving trend followed, leading to runs of about 24 million sockeye as recently as the early 1990s, and it was thought the Fraser was returning to its natural levels of productivity. A downward trend began about 15 years ago, with occasional big runs, leading to this year's nadir.

Both Mr. Angelo and Mr. Reynolds said changes in climate are having an impact, but they noted sockeye are doing well both to the north of the Fraser, in Alaska, and to the south, in the Okanagan River.

Mr. Angelo said more ocean-based research is needed to find out exactly what is depressing the Fraser's returns.

He said participants in the conference "did not rule out [lice from]fish farms," as a possible cause, even though DFO did just that earlier this year.

In a letter to The Globe and Mail, in August, Paul Sprout, DFO's Pacific Region director general, stated: "Sea lice from fish farms are not the explanation for this year's extremely poor marine survival of Fraser River sockeye." Mr. Angelo said DFO declined to participate in the conference because a judicial inquiry into the management of Fraser sockeye salmon is to get under way shortly.

Prime Minister Stephen Harper announced the inquiry last month and Supreme Court Justice Bruce Cohen was appointed to head it.

Mr. Angelo said the government should begin taking steps now to fill research gaps, rather than waiting for the inquiry to conclude.

"There is public concern that little may be done over the next 18 months while the inquiry is under way," he said. "And that would be unfortunate for both British Columbians and B.C.'s salmon stocks if that were to transpire."

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